1. Field of the Invention
The present invention relates generally to a fixing device using the induction heating, which is used for fixing an image, such as a toner image, on a fixed material, such as a paper, in an image forming system, such as an electrophotography system, an electrostatic process copying machine or a laser printer, and a method for producing the same.
2. Related Background Art
Conventionally, there is known the following fixing device for an electrophotography system. That is, a halogen lamp or the like is used as a heat source. This is provided inside of a heating roller of a metal to heat the heating roller. A pressure roller having an elastic material at least on the surface thereof is provided so as to face the heating roller while pressingly contacting the heating roller. A paper serving as a fixed material is caused to pass through a nip portion formed between the two rollers contacting each other. During the passing, a toner image on the paper is melted and fixed. There is also known a fixing device wherein a flash lamp is used for heating a paper without contacting the paper to fix a toner image. Moreover, as fixing devices having improved efficiency, there are known a fixing device having magnetic field producing means combined with a belt as shown in Japanese Patent Laid-Open No. 8-76620, and a fixing device using a heating member of a ceramics as shown in Japanese Patent Laid-Open No. 59-33476.
However, there are various problems in the above described conventional fixing devices. That is, in the fixing device utilizing the induction heating based on an induction coil, it is actually very difficult to uniformly heat the heating roller. In order to optimize the heating efficiency to realize the uniform heating, it is required to optimize the construction of the induction coil itself, but this is actually remarkably difficult.
With respect to the uniform heating of the heating roller, it is also required to prevent the non-uniformity of temperature of the heating roller in axial directions (cross directions) thereof. The conventional device using the halogen lamp heater is designed to cope with it by changing the light distribution characteristics. Also in the induction heating fixing devices, it is required to take measures to obtain the same effects. That is, it is required to take measures to cause heating distribution to be uniform.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a fixing device using induction heating capable of efficiently and uniformly heating a heating roller, easily winding coils onto a core, appropriately fixing on a paper without being affected by the turning ON/OFF of a power supply, and inhibiting the generation of noises, and a method for producing the same.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein going and returning portions of one turn of the coil are spaced from each other by a predetermined distance or more so as to inhibit electromagnetic fields formed by the going and returning portions from being canceled out.
According to another aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil is wound so as to extend in axial directions of the endless member, and a gap between the coil and an object induction-heated by the coil is set so as not to be less than in end portions of the coil.
According to another aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil is wound as a multiplex winding so as to extend in axial directions of the endless member, and a gap between an inside turn of the coil and an object induction-heated by the inside turn of the coil is set to be substantially uniform even in both a central portion and an end portion of the coil.
According to another aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil is wound as a multiplex winding so as to extend in axial directions of the endless member, and a heat generation distribution of an object to be heated is optimized by changing distances between the outermost turn of the coil and other turns thereof inward of a core.
According to another aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through electromagnetic induction coils, which are arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil is wound so as to extend in axial direction of the endless member, and a turn of the coil next to a certain turn thereof is sequentially wound onto the outside of the certain turn, the certain turn having a U-turn portion, at least a part of which is bent so as to have a radius R of curvature, and wherein a relationship between the radius R and a distance D between going and returning portions of the certain turn is set to be a predetermined relationship.
According to another aspect of the present invention, there is provided a method for producing a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil is wound onto an outside peripheral surface of a substantially cylindrical core so as to extend in axial directions thereof, the core having core bodies, onto which a first turn of the coil is wound to be supported, on the outside peripheral surface at two places facing each other in radial directions, each the core body extending in the axial directions, and wherein the first turn of the coil is wound onto each of the core body, and then, the next turn of the coil is wound next to the first turn to sequentially carry out this procedure so that substantially half of the coil is wound onto the outside peripheral surface of the core, and wherein after the coil is wound by the procedure to cover substantially half of the outside peripheral surface of the core with respect to at least one of the two core bodies, the coil is wound by the procedure with respect to the other core body to cover the remaining half of the outside peripheral surface of the core, so that the coil substantially covers the whole surface of the outside peripheral surface of the core.
According to a further aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein the coil has non-central portions of non-dense coil portions on both ends of the. coil in axial directions, and the vicinity of the non-central portions are provided so as to face a fixed portion of the member to be fixed.
According to a still further aspect of the present invention, there is provided a fixing device using induction heating for causing alternating current to pass through an electromagnetic induction coil, which is arranged so as to be close to an endless member having a metal layer of a conductive material, to cause the endless member to generate heat to heat a member to be fixed, wherein two outgoing lines of going and returning portion of the coil are attached to each other.